Pros and cons of soil blocks for seed starting

So, I am making plans for my first semi-commercial farm garden. I hate those silly plastic pots that end up all over, and I am interested in trying soil blocks.
Pros
Hopefully cheaper
Healthier plant roots
No plastic pots
Cons
Finicky soil mix
Fall apart ?
This is what I am finding, and Elliott Coleman makes it look very easy. I have no personal experience, so I'm wondering if anybody has tricks, tips, warnings, endorsements, soil mixes. Or is nobody using these.
Coleman's mix is
3 parts peat
3 parts compost
1 part pearlite
Plus minerals and fertilizer

I have made soil blocks in the past. I went back to little plastic pots. Here's why-

The soil mix does need to be good. I am not one for buying lots of peat moss and such, but I did manage to make a decent on-farm soil block mix using sand, clay, and compost. I dont remember the exact ratios, but it isnt that difficult to get right. It should be more dense and sticky than you would think for potting soil, otherwise it does fall apart.

Thing is, you need a ton of this mix for your soil blocks. The main thing that I was using soil blocks for was tomatoes and peppers, using the 4" blocks. I ultimatley gave up on the soil blocks because if I raised my tomatoes in 50 cell trays, and then transfered to half gallon plastic pots, I could use nice mix in the flats, and then just garden soil in the big pots. This was much easier to deal with.

I never saw better growth in the soil blocks. In fact, I think the half gallon pots grow a better transplant. The plastic trays and pots are reusable for years if you put them stacked in a shed. It is much cheaper using the plastic containers because the mix is so much cheaper.

Just my experience, I still have the soil blockers (2 inch and 4 inch), but I havent used them in years. It works for Elliot, no doubt, but was a disappointment for me. Of course, YMMV.

good luck!

My only experience (at somebody elses' grow shack) was that once you got the soil mixture right (so the pots wouldn't just fall apart), they were so tough that the roots could not penetrate the soil. He ended up with a ton of tiny plants that were root-bound, and none of them ever recovered to become full sized, healthy plants.

As far as the peat is concerned (many people feel that this is not a renewable resource), I have been informed by people living in the peat-bog regions that those bogs are expanding each year. If we (or somebody else) don't 'consume' this product, the peat will overrun millions of acres, making it unsuitable for anything else.

Next, perlite. I hate that shit. It is so light, that every time you water, it floats up. Eventually, almost all of it ends up on the surface, where the wind just blows it away.

I much prefer to use soil flats. Nothing is wasted that way. If a seed doesn't germinate, you only lose the temporary use of 1 square inch of soil. With soil blocks, you need to put 2-3 seeds in each, and select for the healthiest one, clip the rest. One half, to two thirds of your seed is wasted.

I didnt love my soil cube until I used them on a wicking watering mat. Cubes stopped falling apart, root growth in its hunt for water was stronger therefore holding the cubes together better, and I just used a mix of my garden soil and some light potting soil.

It was always the watering that broke the top corners off my cubes.

I only use the 3/4 inch and the 2 inch, and I love them. One tomato seed to one 3/4 inch block is almost no waste if it doesn't germinate and you only go to the 2 inch if you have a growing plant, so I don't understand the waste comment. I would use more soil in a pot than I do a block.

I used the 2" blocks for a couple of seasons and then found the same thing John did - the blocks do not degrade in my climate which is very hot and very dry. I, too, ended up with hard little cubes that stunted plant growth. In fact, I am STILL finding these little cubes in my yard years later. Peat pots don't break down in my climate either - if I should get a plant in a peat pot - I peel off the pot and tear it into tiny pieces and put it into the compost pile.

I live in a temperate, wet climate. I tried them one season (the small ones for starting before potting up) and I had success with them. They made the transition to being potted up well. This year I mixed up seed starter mix and put it into small cell trays and I am not impressed. Many of my plants are having a full on revolt at being potted up. Think that I might go back to the blocks. They are more work up front, but I had a lot more success with getting my plants to the next stage. I haven't tried the bigger blocks. I think the size I was using was 3/4"

Dustin Powers wrote:I didnt love my soil cube until I used them on a wicking watering mat. Cubes stopped falling apart, root growth in its hunt for water was stronger therefore holding the cubes together better, and I just used a mix of my garden soil and some light potting soil.

It was always the watering that broke the top corners off my cubes.

What were you using for a wicking mat under your soil blocks? I've been thinking about making my own out of some unbleached, natural wool fabric. There's a bunch of different synthetic wicking mats (a.ka. capillary mats) out there on the market but I like to use the most natural materials I can. So if anyone has other suggestions (other than newspaper, haha) I'd appreciate it.

I like to use the most natural materials I can. So if anyone has other suggestions (other than newspaper, haha) I'd appreciate it.

Would coco fiber (coir) work?
A waste product, that seems to last quite awhile before it 'returns to the earth'.

I use soil blocks and they work well for me. I use a mix of compost, peat and sand. I don't have much topsoil suitable for starting plants. Just sod and clay. My blocks are a little fragile.

I would not use much clay in a soil block, and if I did, I would not use sand. After all, rammed earth is a compressed mix of sand and clay.

I would like to find an on-site replacement for peat, but haven't had time to experiment yet. In regards to expense, using soil blocks greatly reduces the need to add compost to the soil, so they might use more materials than starter trays, but it is important to look at the complete cost of the system.

I've been using soil blocks for 2 years for vegetable seedlings and I like this system. I feel that it is a little more work to start the seedling, but much less work when it is time to transplant seedlings.

I used 10" x 20" plastic trays in which I can put 40 or 44 2-inch soil blocs. I do not need any other plastic cell pak (so less cleaning to do and less stuff to pile somewhere !)

It needs some practice to find a good mix. Many will work, but I usally use a mix of commercial mix inoculated with mycorrhizae, compost and coco coir. I found that coco coir is really helping to maintain the sturdiness of soil blocks, especially for big 4" blocks. The right amount of water in the mix is also critical so the block won't fall apart.

I do not know if seedlings are healthier with soil blocks than with regular trays/pots, but I know that they are very healthy. They are sturdy, easy to manipulate and easy to water (just pour water in the 10x20 trays). I have not seen any difficulty for the roots to grow in the soil blocks.

I tend to use less often 3/4 inch blocks as I feel that it is more work and germination rates are already high in 2" blocks. For tomatoes, I use the longest pin with 2" block and I put the seed in the hole. As the plant (and its main stem) grows, the stem inside the hole seems to make roots and the seedling is quite sturdy.

David

I've had good results from making soil blocks. I also don't like using plastic trays and find after a few years that they break apart and I have a constant inner struggle whether to use them again in damaged state or finally buy new ones.

I have made them with peat and coco peat. Both have worked well, though I personally want to find a local solution because importing those materials just brings up the cost and emissions of what I grow. I have read about making a degraded leaf litter as a peat replacement, but haven't tried this yet.
Here's a similar thread with good suggestions: https://permies.com/t/7049/organic/Soil-Block-Makers-Eco-conscious

I'm wondering if sod of some type could be put under cover to die off, then used as soil blocks. The root mass ought to hold things together, and eliminate some of the need for exotic ingredients. If nitrogen fixers were included in the sod, that would be a further advantage.

Now I'm thinking; what if in the Fall we laid out several inches of compost, and planted clover or some other such plant in it, along with an annual grass. Then, we would cut the "sod" up into blocks and put them under cover to dry out and die. Come spring, could we rehydrate these and use them as soil blocks?

If a little clover came back, that would not necessarily be a bad thing.

I really liked using my soil blockers. First time using them this year, and was very pleased with the results. I had to start things inside under lights and heat, so had very little space, and the 3/4" blocks were great for that. Lots of things started in a very small space. I potted up to the 2", and by that time I could spread things out more, as they didn't need the bottom heat after germination. By the time it was time to pot up the tomatoes, I used recycled 6" pots I got at the free store, and could put them outside in my little greenhouse.

I used the soil mix recipe from Eliot Coleman's The New Organic Grower. In that mix he advocates using sharp sand, not perlite. I generally used what I had - not-sharp sand, some used seasoil, compost and peat moss. I added amendments such as rock dust, greensand, lime, and some organic dried seaweed stuff. It worked great. The blocks held to gather well, and everything grew very healthy and strong. Misting is definitely the way to go with the 3/4" blocks, and the first few days of the 2" blocks. But once the roots have infiltrated the blocks, regular light watering worked well; although, I can definitely see the advantages of using some sort of capillary mat to water, as you would not have to be quite as diligent in keeping them watered.

All in all I was very pleased with the results. I think that experimenting with things like worm castings and leaf mould will be in order in the future. Anything that is nutrient rich, holds water, and holds together well should work brilliantly. I'd definitely like to be using only on-site materials as soon as possible. So, hopefully in the spring I'll have everything I need - compost, sand, garden soil, worm castings, leaf mould - and I'll have a go at using different mixes to see what works best.

Oh, how I love experimenting!!

I just started using soil blocks last year, and I can say I won't go back to pots. "Potting" up is a breeze, and I save so much more space and time over traditional seed cells and pots. I think others here were having issues because they either mixed clay and/or let their blocks dry out. As long as the blocks stay moist they don't harden at all and can be crushed easily with your hands. Leaf mould, vermicompost, and a bit of wood ash will do the trick for a great mix. You could mix some sand in there to add more aeration if that becomes an issue.

I would avoid Peat moss for a multitude of reasons. My primary concern is it just doesn't absorb and distribute water properly, therefore requiring a host of other ingredients to compensate (perlite, vermiculite, etc). Even with perlite, the Peat blocks I made tended to dry out and harden readily. I switched to coco peat with vermicompost, which worked much better than the Peat moss. The vermicompost held everything together perfectly, but you need to make sure your moisture is right when creating the blocks.

This year I'm experimenting with well rotted pine. After sifted, It's about the same consistency as the "Coco Peat" but free and readily available for me. It's also inoculated with Mycorrhizae and should theoretically contain a better mineral mix. I just started some onions in the 3/4 inch blocks, I'll post an update here and let everyone know how it goes.

Pros:
Free after initial investment
No plastic
Less space (no plastic taking up storage, or cell space)
Less water (if done right the blocks absorb and hold on to water better than plastic pots)
Faster transplanting and potting up
Less transplant shock

Cons:
Higher initial investment
Takes some time to get the consistency and mix right
Won't work with garden soil (clay will turn these into hard rocks)

An idea for wicking mats, born of necessity: I used cardboard with the edges turned up and stapled. One extra sheet of cardboard inside for more absorbency. What Dustin mentioned above I agree with, the roots are seeking downward. I used 2" blocks and no perlite, just commercial potting soil and a little dirt, and they have held up ok. I didn't read John Polk's advice before buying it, so I will figure out what to do with it. I think I am going to try to Unfortunately can't do a RMH.


Once the plants are bigger, staples come out and the cardboard will be used in a sheet mulch for some of the same plants.

I grow mostly perennial plants to sell. I start all seeds in these white polyboxes you get at the greengrocer and then use the nasty plastic pots and hope to get back as many as possible. When I ws a kid gardeners used to sell lettuce seedlings in a big block which they cut up with a knife, the seedlings wrapped in newspaper. Unfortunately all degradable pots are too expensive.

So, I've been trying soil blocks without much success. My biggest issue is that the seeds fall off the blocks into the cracks, the roots all grow together and I'm spending a lot of time teasing apart seedlings. Germination has been good on a few varieties of plants, like turnips, and virtually nil on others, like onions. They require a lot more water, and more frequent watering. I would really like to get away from plastic pots, for multiple reasons, but I'm getting frustrated.

I used almost exclusively soil blocks this spring; 100 tomato plants, many peppers, some brassicas, lettuce, and other things.

Overall, I liked it. The total absence of transplant shock, even under bad conditions, was great. Some batches disintegrated a bit; (the consistency and moisture level of the mix is important) and watering them was difficult. I found that by lining a tray with plastic and flood irrigating them, it worked a lot better.

I found a lot of useful information in this thread. I'm elevated with this, but I still have some questions/ideas lingering:

Root development with seedlings

Mold

Seeding depth

Success rates

I was hoping some more experienced of you could help me validate my ideas.

Root development
Smaller seeds like Pak Choi and Kohlrabi don't seem to develop roots deeper into the block. I'm using peat moss / compost / perlite in 1:3 ratio each. I used 1.6 inch blocks (4 cm). I put the seeds in to the hole (0.3 inch / 0.8 cm deep). I did not cover seeds with anything, just pressed them slightly against the block. The seedling are so weakly attached to the blocks that they easily fall over.

Mold
I observed mold development on the blocks. I used both fresh peat moss and compost as well as oven-sterilized substrates. Same result, only that the sterilized mix took longer time to mold. The important bonus with sterilized mix is the total lack of damping-off disease.

Seeding depth
Seems like it's better to drill a seed-sized pocket in the block. If the pocket made with the dibble is too large the seed has issues as described above. Alternatively, seeds need some cover (vermiculite, soil). Otherwise, even with damp/moist blocks the seeds take longer to germinate and require more watering. And this causes other issues.

Success rates
I tested this with four batches:

nonsterilized mix blocks - survival rate 9 out of 24 sample batch blocks (37%)

sterilized mix blocks - 83 out 100 blocks. This includes Sage which germinates longer.

traditional potting container but with the same sterilized mix: 58 out of 64 seedlings that I started in the same sterilized mix, but in traditional way - a flat potting container, 10 seedlings in a row, closely spaced, to be transplanted later to larger pots.

damp kitchen cloth (I'm starting seeds in a damp warm cloth and then transplant once they germinate into the mix): almost 100% germination rate. I didn't count as a I've thrown handfuls of seeds leftover from previous batches (:. I'm still waiting to transplant these into potting medium, but the results are promising.

There is some bias, though: with each batch I'm getting more experience with temperature and watering and I water seedling with greater care. Also, I'm a newbie, with no complete education, I'm just experimenting with whatever seemed reasonable and cool at the same time

I started using soil blocks this year, I used the Eliott Coleman recipe, except I substituted the compost for worm castings and the perlite and lime with biochar, I did not include fertilizer in the seed starting mix, only in the "potting up" mix. I've also tried them with a commercial peat based mix.

Root pruning from the bottom doesnt seem to work that well ? I find the root will continue to grow laterally for some time, I'm buying a gridded tray today that I can put over a gridded shelf. I'm hoping the combination of actual air space and light will do of better job at air pruning.

Root pruning on the sides works okay, but sometimes they will latch on to a sister block and can get a bit out of control.

They dry quickly, so a capillary mat might be a good idea, I've been misting the 3/4 blocks and bottom watering the 2 inch blocks, I wonder if the air pruning would work with a thin capillary mat and an aerated shelf, but I worry the roots would get stuck in the mat.

It's annoying that you need to have the right soil mix, but it's cool to make your own.

Using the 3/4 blocks to start the seeds means it doesnt take much space or potting mix to start an ungodly ammount of seeds. Useful if you're starting seeds with long germination times.

My old method, which was mass seeding a small pot then separating seedlings by hand, worked well, but induced a lot of transplant shock, this eliminates it completely ! (IF you dont wait too long to transplant once the roots reach the sides.)

Utimately, I do think there might be a better way, but I'm enjoying my soil blockers for now. I think a good alternative would be to have a  tray lined with tiny smart pots. The side walls of the tray would have to be deeper than the height of the pots to allow air pruning, but it would make handling easier and remove the need for a specific soil mix. You could have trays with different pot sizes and a cover that could make a dimple the size of the previous tray. All I've seen on the market generally only air prunes the bottom and does not come in different sizes (generally they are too small). They are also all made of bad plastic that would clearly break after a year or two.

Peter Smith wrote:   So, I am making plans for my first semi-commercial farm garden. I hate those silly plastic pots that end up all over, and I am interested in trying soil blocks.
    Pros
        Hopefully cheaper
        Healthier plant roots
        No plastic pots
    Cons
        Finicky soil mix
        Fall apart ?
  This is what I am finding, and Elliott Coleman makes it look very easy. I have no personal experience, so I'm wondering if anybody has tricks, tips, warnings, endorsements, soil mixes. Or is nobody using these.
    Coleman's mix is
3 parts peat
3 parts compost
1 part pearlite
Plus minerals and fertilizer

I saw some commercial farmers carrying around a very solid, heeavy duty 10 x 20 seedling tray, like 72 cells if I recall.  They push them out from the bottom I think. They pop right out and I bet those trays last forever.  I think they are the correct size where they can sit in a 10 x 20 tray for watering.  They pop it out and throw it in the hole from a distance , with the tray dangling downwards in one hand the entire run of 72 cells.

To me the soil blocks seem like a lot of work.

I'm a newbie gardener and used soil blocks for my first time doing seedlings. I used the Coleman recipe with some adjustments. I used my homemade vermicompost (instead of finely sifted regular compost). I had dried out this compost by leaving it in the sun last year (won't do that again), so it had clumped into small dry pieces. I added some water, and ran it through a Vita-mix blender to make it fine and somewhat smooth. However, at this point, Coleman's recipe did not produce a mix that held together well enough to be made into blocks. So I kept added small amounts of clay (modeling/craft clay on one batch, our clayey garden soil on another) till it would hold together.

I had good results with both 3/4" (micro) blocks and 2" blocks. I mostly bottom-watered except for the micro blocks which I spray misted. When I went away for a week, I used a capillary mat fashioned out of Bounty (only for 2" blocks).

I used the micro blocks only for tomato seedlings, which I "potted up" to 2" blocks. It worked well, but I wonder if this two-step was really necessary.

NOW MY QUESTION: What has people's experience been with 4" blocks? That block-maker is kinda pricey so it would be good to have some feedback. I'd want to promote my tomato seedlings from 2" to 4" blocks, instead of cut-off half-gallon milk cartons as I'm doing now, in order to avoid root-bound seedlings.

I've had mixed results, some 4" blocks are holding up great and I'm seeing good growth in the plants. Others not so much, they seem to be unable to send roots from the 2" into the 4" block. While they generally end up managing it, there growth slowed down and some of them got stunted. I think I waited too long to transplant them and those blocks that fared the worse had improper aeration underneath them, meaning they had sent out roots outside the blocks.

Once I'm done with some specific gardening tasks, I'll do a test run comparing the soil blocks to these new trays I just got; the neversink farm winstrip trays: https://www.neversinktools.com/collections/winstrip-trays as it seems like I could get the best of both worlds this way.

I started hundreds and hundreds of seedlings this year for my meadow and food gardens and used a variety of means to start the seeds.  I like soil blocks for some things. It depends on what you are growing. In my experience:

Germination method: Soil blocks (2") work best for plants that do not have deep roots and do not grow quickly - things like grasses and alliums. I start plants that do not necessarily germinate well, will need to be up-potted and do not quickly create a taproot (like peppers and herbs) in small flats of soil, then just use a spoon to separate them when I am up-potting them.  It's a very simple and quick method, and I have had no issues with seedlings not surviving the up-potting process. For plants that get big quickly and germinate well (like tomatoes), I seed directly into 4" pots.  For seeding deep-rooted plants (like many widlflower perennials and biennials), I use a 5" deep 50-cell tray. Using the deep trays eliminated the up-potting process for most of my wildflowers.

Soil: The soil blocks do need a mixture that contains some, but not too much, compost in the soil to hold them together.  I have learned the hard way that your soil has to be sterile however.  I had too much trouble with diseases and pests using non-sterile soil, and, sadly, even the soil I sterlized myself had issues. Cheap ol' me now buys all of the soil mixtures that I use to start seeds in.

Watering:  Soak the soil well before putting it in the tray.  Water the seeds while they are germinating and when they are newly sprouted with a mister to prevent the seeds or the seedlings from dislodging. Misting is especially important for small seeds or seeds that you didn't bury.  If you have to during this time period, bottom water carefully.  The soil blocks can melt, so to speak, if you put too much water in the tray at once. Once the plants are strong enough, you can water from the top. Once the plants have germinated, water once the soil on the top is dry (stick your finger in it to check), then water deeply enough that all of the soil is soaked. If you are having problems with mold or damping off, you are watering too much and/or the soil wasn't sterile. If the roots do not grow all the way down to the bottom of the pot/block, you are not watering enough when you water.  A combination of mold and shallow roots would indicate you are watering too frequently and not uisng enough water when you water. Conversely, if almost all of the roots are at the bottom of the pot, you are watering deeply but not frequently enough.

Fertilizer: I do use a liquid fertilizer for my seedlings.  My plants do so much better with supplemental food, even if the soil does have compost in it. Note too that some soil mixes provide no nutritional value to plants (for example, peat), so how much you fertilize does depend on the soil you've used.

Protection: I started a number of my seeds outdoors last fall and left them on the back porch all winter to stratify them.  Be aware that some critters like to eat seeds and/or seedlings, so they may need protection. I've had mice eat my seeds and I've had birds pull up my seedlings. Bunnies and deer will munch on tender shoots even if they would never eat the mature plant. I now elevate my seeds and cover them with row cover to protect them while they are young. For the mice - mousetraps work well, but you need a box over the trap with holes cut in the box so mice can get in but not birds. Thankfully, there's a cat that lives in my woods that comes to clean out my mouse traps every day :)